A receptacle cap, which is generally used to immediately add additives to contents in a receptacle when the receptacle cap is opened, so even additives that spoil easily may be stored in a fresh state and then added right to the receptacle contents before drinking, has been developed as Korean granted utility model no. 20-0360704.
Further, receptacle caps which hold additives inside and the contents in the receptacle may be drunk together therewith have been developed as Korean granted patent no. 10-1344480, Korean granted patent no. 10-1342876, and Korean granted patent no. 10-1499752. Korean granted patent no. 10-1344480 has a problem of difficulties in long-term storage due to its sealing plate being permeable, and Korean granted patent no. 10-1342876 does its sealing using an aluminum seal, so the permeability problem is modified, but because a separate assembly device needs to be added, there are problems of having poor assembling properties and being fragile to external impact. Also, Korean granted patent no. 10-1499752 is easy to assemble and use, but it is difficult to put in contents that require sterilization at 70 to 80 degrees Celsius because of its low heat resistance.